Liquid crystal display panels of active matrix type drive system include, for example, an active matrix substrate (also referred to as TFT array substrate) that includes thin film transistors (hereinafter referred to as TFTs) disposed in individual pixels as switching elements, where the pixel is the smallest unit of an image; an opposite substrate disposed facing the active matrix substrate; and a liquid crystal layer interposed between these substrates.
The active matrix substrate can be inspected in two ways: one is the electrical inspection conducted on a large unseparated active matrix substrate, and the other is the optical inspection on individually separated panels.
An individually separated panel can be examined for defects by comparing the light amounts transmitted under the light projected from a backlight or the like, while voltages are applied to the liquid crystal layer interposed between the active matrix substrate and the opposite substrate.
However, defects found on the active matrix substrate may not be repaired perfectly due to the presence of the opposite substrate. Also, any foreign matter generated as a result of the repair can remain inside the panel, which can lead to another defect.
Defects found on a large unseparated active matrix substrate can, in many cases, be completely repaired. Any foreign matter generated as a result of the repair can be removed, and the alignment film is not damaged, because the repair process in this case handles only the active matrix substrate.
Also, when an inspection is conducted on a large unseparated active matrix substrate, because the inspection is conducted shortly after the manufacturing of the active matrix substrate, useful information for tracking and reflecting the manufacturing process conditions can be obtained, and that information can be used for quality control.
Inspection of a large unseparated active matrix substrate can be conducted in methods such as the array inspection method, where electrical charge amount inputted to individual pixels is read out via a reverse path, and the contactless inductive power transmission method (abbreviated as IPT), where the voltage value at the pixel electrode is read out by placing a needle-shaped electrode very close to the pixel electrode but without touching it.
Array inspection, however, is used for display devices that are mainly for compact and portable applications. This is because, due to development trend of those display devices to increase a number of pixels formed in the same space, i.e., higher resolution, the needle-like electrode used in the IPT inspection method does not have an appropriate size to match the fine pixel pitches.
Both the individually separated panel and the large unseparated active matrix substrate include a wiring pattern called short ring in the frame region of the active matrix substrate. Short rings are provided to prevent the electrostatic breakdown caused by the static generated during the manufacturing process.
The short ring is connected to the gate lines, source lines, capacitance lines, power supply lines, control lines, and the like to prevent electrostatic breakdown that can occur during the substrate handling before or after processes such as attaching the alignment film, rubbing, bonding the substrates, and glass cutting. Normally, the short ring is removed in the scribing process or chamfering process after the panel is assembled.
For example, Patent Document 1 discloses a large unseparated active matrix substrate with a short ring formed thereon.
Patent Document 1 states that, as shown in FIG. 8, the short ring can be cut off during the manufacturing process of the liquid crystal display device after the process prone to be influenced by static electricity is complete, by cutting off a conductive short ring 114, which is electrically connecting terminal sections 113 of respective wiring lines to each other to equalize the potentials of the transparent electrodes and the wiring lines, using a laser beam radiated through a transparent substrate 111.
The short ring 114 is constituted of a band-shaped main line 115, which is disposed along the frame region of the transparent substrate 111, and numerous branch lines 116 that branch off from the main line 115 and that are connected to terminal sections 113 of respective wiring lines disposed on the transparent substrate 111.
Patent Document 2 discloses a large unseparated active matrix substrate with a short ring formed thereon.
As shown in FIG. 9, a conductive adhesive 123 is applied to at least one of a connection pattern 118 and a substrate connection pattern 121, the element substrate and the opposite substrate are bonded to each other face to face, and the conductive adhesive 123 electrically connects the connection pattern 118 and the substrate connection pattern 121 to each other.
As a result, according to Patent Document 2, a wiring layer 117 and an opposite electrode 119 can have about the same potential, and therefore breakdown of elements and damages to wiring lines and opposite electrode due to the electrical discharge between the two substrates can be prevented.
The opposite electrode 119 is connected to a region connection pattern 120, which is disposed to border each region into which liquid crystals are to be sealed. Further, the region connection pattern 120 is connected to the substrate connection pattern 121.
Patent Document 3 discloses a separated active matrix substrate with a short ring formed thereon.
As shown in FIG. 10, all or some row electrodes 127 and column electrodes 125 on the substrate are electrically short-circuited throughout all processes or some processes that are to be conducted during the time period starting immediately after the process in which two substrates 124 and 126 are bonded together and then are cut and separated into a prescribed shape, and ending before the connection to the driver circuit is established.
Because the row electrodes 127 and the column electrodes 125 are electrically connected with a conductive resin 129, static electricity does not unevenly build up on any particular electrode. This way, according to Patent Document 3, electrostatic breakdowns that can occur in active matrix type electrooptical devices after the cut and separation process can be prevented very easily, and the production yield can significantly be improved. The two substrates 124 and 126 are bonded together with an adhesive layer 128.